Catalysis in Confined Spaces of Metal Organic Frameworks

Abstract

Compared to homogeneous catalysis, heterogeneous catalysis can achieve product selectivity due to spatial constraints and differences in molecular dimensions of substrates and products by performing the reaction in a confined space. Shape selectivity for substrates, products or transition states is a wellestablished phenomenon observed in porous inorganic solids like zeolites with considerable impact in petrochemistry. More recently, metal organic frameworks (MOFs) have emerged as heterogeneous solid catalysts for a broad range of organic reactions due to their unique properties of large surface area, tuneable pore volume and high density of sites. The present mini-review aims to describe the current evidences showing MOFs as shape-selective catalysts. After a brief introduction on the concept, types and examples of shape-selectivity, the available data on MOFs as shape-selective catalysts have been organized according the nature of active sites promoting the reaction, starting from metal nodes as Lewis acid sites and commenting examples of encapsulated metal nanoparticles (NPs) and molecular guests as centers in various reactions such as addition to carbonyl compounds, hydrogenations, oxidations and oxidative dehydrogenations. The final section provides our view on the current achievements and prospective for future developments in the field.

Copper(II)‐Doped ZIF‐8 as a Reusable and Size Selective Heterogeneous Catalyst for the Hydrogenation of Alkenes using Hydrazine Hydrate

“…[55,56] As commented earlier, size selective hydrogenations have been reported with noble metal NPs encapsulated over MOFs like ZIF-8. [23] Hence, one of the main objectives of this work is to demonstrate the catalytic activity of Cu 2 + ions in the size selective hydrogenation of olefins under mild reaction conditions without the requirement of noble metal NPs. Interestingly, the framework Cu 2 + ions promote the hydrogenation of olefins while ZIF-8 offers a confined environment to achieve size selective catalysis.…”

“…[18][19][20][21] Inspired by these research findings, many research groups have focused on the encapsulation of metal NPs over MOFs and their activities are examined in the size selective catalysis. [22,23] One of the prerequisites of MOFs to behave as hosts for metal NPs is their stability during the loading of metal NPs. In this aspect, metal NPs encapsulated over MOFs have been reported as heterogeneous catalysts for the size selective hydrogenation of olefins using Pd nanocubes@ZIF-8 under photocatalytic conditions, [24] Pd@ZIF-8, [25,26] Pt@ZIF-8, [27] Pt@ZIF-8 with different particle size, [28] Pt/UiO-66, [29] SIM-1@Pt/Al 2 O 3 (SIM: Substituted Imidazolate), [30] PtÀ Cu frame@HKUST-1 [31] and RhCo-Ni@ZIF-67(Co)/RhCoNi@MOF-74(Ni).…”

Cucurbit[7]uril as Nanoreactor for the Fixation of CO2 with Oxirane: A Density Functional Theory Investigation

“…Moreover, confinements have been considered a powerful tool among researchers to modify the structure, electronic properties and efficiency of the catalyst. Also, confinement (or confined) catalysis has gained vast interest in heterogeneous catalysis as it influence the reactivity [25–47] . Presently, confined catalysis has been widely used for the catalytic conversion of CO 2 into useful chemicals [48–51] .…”

Barrier-free liquid condensates of nanocatalysts as effective concentrators of catalysis

“…Once the limit in catalytic efficiency is achieved from the variations in shape and size of catalytic materials in the nano-regime [1] , interests to amplify the efficiency further are switched towards the spatiotemporal confinement of nano-catalysts [2] . Microenvironments in the form of molecular vessels or crucibles of different architectures like core-shell structures, porous materials, 2-dimensional materials, and organic casings have been developed that demonstrated enhanced catalytic properties [3][4][5][6] . Furthermore, caging helps to isolate nanocatalysts in a solution.…”